In the field of high explosives it is often necessary to shape the detonation shock wave to a prescribed pattern. If a point source is used to detonate a right cylinder of explosive material, the shock wave will propagate through the cylinder in a spherical pattern. The exiting shock wave will be spherical as well. If the desired shape of the shock wave is planar, then a lens must be used to reshape the wave.
One of the most common ways to convert a point source shock wave into a plane wave is by tailoring the shape of the explosive material. A typical explosive plane-wave lens includes a first cone made of a low velocity detonation material such as baratol (a mixture of barium nitrate and TNT). The flat portion of the cone is positioned against the device for which the user intends to transmit a planar wave. A second detonation material having a high detonation velocity is cast over the baratol and machined so the outside contour is cone shaped. In operation a detonator is used to initiate the high detonation velocity explosive at the apex of the cone. By the time the wave has reached the flat end of the cone, the shock wave is planar. This method is described in U.S. Pat. No. 2,604,042.
There are a number of severe drawbacks to tailoring the shape of a shock wave by shaping the explosive material. The first drawback to the above-described approach is that it is extremely costly to machine explosive material. In the plane-wave device described above, the baratol is first cast and then machined to high tolerances. A second material is then over cast and again machined. This repeated machining of explosive material requires special remote controlled machinery to insure safety. There are few machine shops which have the proper equipment to machine explosives in this way.
Another difficulty with standard plane-wave lenses is that approximately two-thirds (2/3) of the raw explosive material is wasted in the machining process. Because baratol has a significant barium component, the wasted material is toxic and must be disposed of in a safe manner. The standard plane-wave lens is, therefore, expensive and potentially dangerous to the environment.
Baratol is not a highly controlled substance and, therefore, has varying properties batch-to-batch. Because it is often necessary to have maximum variations of 0.2 .mu.s in the time of arrival of a shock wave, each batch of baratol must be analyzed and new calculations must be undertaken to determine cone angles (.alpha. and .beta.) of the baratol and the second explosive. The relative velocities of the two explosives allow a plane wave to be formed. If the baratol has varying detonation velocities, it becomes difficult and time consuming to produce a uniform quality product.
It is therefore an object of the present invention to provide an explosive plane-wave air lens which does not require expensive machining of explosive material.
Another object of the invention is to provide an explosive plane-wave air lens which can be fabricated without generating toxic waste.
Another object of the invention is to provide an explosive plane-wave air lens which has repeatable and reliable performance.